GeoGraph - photograph every grid square

The lock seen here is Marsworth Top Lock, which give access when travelling in this direction (eastwards) to the Tring Summit Level, the highest stretch of canal on the Grand Union Canal. Water fed into the summit level supplies the rest of the canal in both directions. The water is supplied by four reservoirs, SP9213 : Startopsend Reservoir, SP9213 : Marsworth Reservoir, SP9113 : Tringford Reservoir & SP9013 : Wilstone Reservoir (see also SP9013 : The heron waits at Wilstone).
The building immediately behind the lock is a dry dock for work on canal craft, entrance to this dry dock is also by means of a lock, which once shut a sluice at this western end can be opened to drain the dock.